The present invention relates to a filter apparatus having a plurality of essentially horizontally disposed filter zones that are disposed one above the other in the direction of a vertical central axis of the apparatus, with at least one common unfiltered fluid channel for the supply of a fluid that is to be filtered (unfiltered fluid) as well as at least one common filtrate channel for withdrawing filtered fluid (filtrate) being associated with the filter zones, each of which has at least one filter sheet, which is provided on a filter element, serves for the deposition of at least one cake layer formed from at least one filtering aid, and separates a filtrate collection area that opens into the filtrate channel from a filter or filling space disposed above the filter sheet, with the apparatus also having a respective annular distribution space for each filter zone, each distribution space extending about the central axis, opening at its periphery at a greater first radial distance from the central axis into the filling space via discharge opening means, and, at a lesser, second radial distance from the central axis having at least one inlet opening means, for unfiltered fluid, that is in communication with the unfiltered fluid channel.
Pursuant to one known filter apparatus of this general type, which is in the form of a filter press (German Offenlegungsschrift 36 17 519), a respective distribution space as well as a filling space is provided between the horizontal filter elements and the filling structure. Each filling space is separated from the associated distribution space disposed thereabove by a wall or wall portion that is in the form of a guide plate, and communicates at the periphery of the guide plate with the filling space disposed therebelow via a slot-like opening that is formed there. In the region of the vertical central axis of the filter, each distribution space, at its upper boundary, which is formed by the underside of the respective filter element disposed thereabove, is provided with an inlet opening means that is disposed across from the center of the guide plate and that is connected to the unfiltered fluid channel via a connecting channel that is formed in this filter element, extends radially relative to the central axis of the filter, and extends over half of the diameter of the filter element, as a result of which it is very long; the unfiltered fluid channel is offset relative to the central axis of the filter and is disposed on the outer periphery of the filter elements. In a similar manner, with this known apparatus each filter element (with the exception of the uppermost filter element) is provided in the region of the central axis of the filter, and above the filter sheet, with a filtrate outlet that similarly communicates with a filtrate channel via a relatively long connecting channel that extends radially relative to the central axis of the filter; the filtrate channel is again radially offset relative to the central axis of the filter and is formed on the outer periphery of the filter elements. Due already to the aforementioned long connecting channels, this known filter apparatus is structurally relatively complicated. Another drawback of this known filter apparatus is that in view of the direction of flow of the unfiltered fluid that enters into the respective distribution space, which flow is in the direction of the central axis of the filter and extends downwardly from above, the guide plate that is provided below the inlet opening must have a relatively large diameter in order to prevent turbulence or washing away of the cake layer of filtering aids that is formed on the respective filter sheet. The slot-like opening, which is formed on the periphery of the guide plate and connects the distribution space With the filling space that is disposed therebelow, is therefore relatively small, so that a relatively high flow velocity results in the region of the slot-like opening for the unfiltered fluid that circulates about the guide plate. A further drawback of the heretofore known filter apparatus is that in order to clean the filter zones, i.e. in order to remove the filter residue, a separate channel is provided in which the filter residue that is loosened by a flushing agent, together with this flushing agent, are withdrawn via a respective slot-like outlet having a relatively small cross-sectional area. The removal of the filter residue requires a relatively long period of time and a large quantity of flushing agent. Due to the relatively small cross-sectional area of the slot-like outlet, there furthermore exists the danger that these slot-like outlets can easily become clogged, especially if during removal the filter residue is not completely dissolved in the flushing agent, but rather forms clumps or the like.
It is an object of the present invention to provide a filter apparatus of the aforementioned general type that, although it has a simplified construction, not only assures an optimum manner of operation, in particular also with a higher quantity throughput, but also enables a simplified and rapid cleaning.